Solid oxide type fuel cell-use electrode support substrate and production method therefor

ABSTRACT

Disclosed is an electrode support substrate for a fuel cell which is even, gives a small fluctuation in gas permeability, and is capable of carrying out printing of an anodic electrode with high adhesiveness, and which comprises a ceramic sheet having a porosity of 20 to 50%, a thickness of 0.2 to 3 mm and a surface area of 50 cm 2  or more wherein the variation coefficient of measured values of the gas permeable amounts of areas measured by the method according to JIS K 6400 ranges from 5 to 20% and further the surface roughness measured with a laser optical manner three-dimensional shape measuring device may be 1.0 to 40 μm as the maximum roughness depth (Rmax) thereof.

TECHNICAL FIELD

The present invention relates to an electrode support substrate for asolid oxide type fuel cell. In particular, the present invention relatesto an electrode support substrate for a fuel cell, which is even in thesize and the distribution situation of pores all over the surface of thesubstrate, which is even and good in the permeability/diffusibility ofgas and which makes it possible that when an electrode or an electrolyteis formed on a single face of the electrode support substrate by screenprinting or the like, the printed electrode or electrolyte is madeexcellent in evenness and adhesion, and to a useful process forproducing the same.

In this specification, an electrode support substrate includes anelectrode-forming substrate having, on a single face thereof, a formedanodic electrode layer or a solid electrolyte film. The substrate has afunction as an anodic electrode in itself and is a support substrate forconstituting a cell by forming a solid electrolyte layer and a cathodicelectrode layer successively on the support substrate itself. In thepresent invention, these are referred to as electrode supportsubstrates.

BACKGROUND ART

In recent years, attention has been paid to fuel cells as clean energysources. The use purposes thereof are mainly power generation for homeuse, power generation for business, power generation for automobiles,and others, and researches for improving the cells and making the cellspracticable have been rapidly advanced.

A typical structure of solid oxide type fuel cells is basically a stackobtained by stacking a large number of cells wherein an anodic electrodeis formed on one face side of a planar solid electrolyte self-supportingfilm and a cathodic electrode is formed on the other face side. In orderto make the power generation performance of the fuel cells high, it iseffective to make the solid electrolyte self-supporting film dense andthin. This is based on the following reason. The solid electrolyteself-supporting film needs to have denseness for blocking the mixing ofa fuel gas which is a power generation source with air surely, and anexcellent ionic conductivity capable of suppressing electric conductanceloss as much as possible. For this purpose, the film is required to beas thin and dense as possible. Moreover, a large stacking-load isimposed on the solid electrolyte self-supporting film since a fuel cellhas a structure wherein a cell having an anodic electrode, a solidelectrolyte self-supporting film and a cathodic electrode and aseparator for separating and circulating a fuel gas and air arealternately stacked many times. Additionally, the operation temperaturethereof is about 700 to 1000° C.; thus, the fuel cells receiveconsiderable thermal stress. Accordingly, the fuel cells are required tohave high-level strength and thermal stress resistance.

From the viewpoint of such required properties, a ceramic sheet mademainly of zirconia is mainly used as the material of the solidelectrolyte self-supporting film for a solid oxide type fuel cell. Acell, wherein anodic and cathodic electrodes are formed on both faces ofthe sheet by screen printing or the like, is used.

The present inventors have been advancing research on such planar solidelectrolyte self-supporting films for solid oxide type fuel cells forsome time, and the research has been advanced so as to aim to make thethickness as small as possible for the purpose of decreasing ionicconductance loss while keeping physical properties and shape propertiesresisting stacking-load or thermal stress (preventing cracks based onlocal stress by decreasing undulations, projections, burrs and others)and, further, so as to aim to make the surface roughness appropriate forthe purpose of heightening evenness and adhesion of the printedelectrode. Previously, the present inventors suggested techniquesdisclosed in JP-A 2000-281438, JP-A 2001-89252, JP-A 2001-10866 andothers.

These techniques made it possible that the solid electrolyteself-supporting film is largely thin and dense, and further the strengthwhich resists stacking-load generated when cells are stacked, thethermal stress resistance, together with the adhesion and evenness ofprinted electrodes, are largely improved by improving the shapeproperty, that is, decreasing undulations, projections, burrs andothers.

Subsequently, the present inventors have been advancing research inorder to improve the performance of fuel cells. This time, research hasbeen made to aim to modify the property of electrode support substratesfor support film type cells instead of the modification of the propertyof ceramic sheets used as solid electrolyte self-supporting films. Thisis based on the following reason. Ceramic solid electrolyteself-supporting films are more easily cracked by stacking-load as thefilms are made thinner; therefore, there is naturally generated alimitation in making the films thin and there is generated a limitationin decreasing in the ionic conductance loss.

In order to obtain cells having structure strength suitable forpractical use in the case that thin solid electrolyte films are usedtherein, electrode support substrates are jointed, as supporting membersfor the cells, in between the cells or their electrodes are caused tohave a sufficient thickness. The substrates have electrical conductivityfor electric conduction. Furthermore, the substrates are made of porousceramic material through which a fuel gas that becomes a powergeneration source, air, or exhaust gas (carbon dioxide, water vapor andothers) generated by burning these gases can permeate and diffuse, whichis different from the above-mentioned solid electrolyte self-supportingfilms.

In recent years, the following method has also been investigated. Amethod of forming an anodic electrode on a porous electrode supportsubstrate by screen printing, forming a solid electrolyte film thereonby coating or the like, and further forming a cathodic electrode thereonby screen printing or the like to produce a cell, thereby making thesolid electrolyte film still thinner so as to decrease electricconductance loss still more.

The most important theme when such a method is realized is that a cellhas even and excellent gas permeability/diffusibility throughout itselectrode support substrate. This is because this support substrate mustbe a porous substrate having pores sufficient for allowing a fuel gasand others to permeate and diffuse through the substrate. Further, thesubstrate is desired to have an even distribution state of the pores insuch a manner that the gas can permeate and diffuse evenly through thewhole of the substrate.

Another property desired for the electrode support substrate is that asuperior printing adaptability is given to the surface thereof so thatan electrode wherein the number of defects is as small as possible canbe printed. As described above, the electrode support substrate isrequired to have an appropriate electrical conductivity. Further, thesubstrate must be a porous substrate having pores sufficient forallowing a fuel gas and others to permeate and diffuse through thesubstrate. Thus, numerous openings are present in the surface thereof.Therefore, in order to make superior electrode-printing possible inspite of the presence of such openings, it is indispensable to clarifysurface properties peculiar to the porous electrode support substratesince the surface properties prescribed about the above-mentioned densesolid electrolyte film cannot be applied, as they are, to the porouselectrode support substrate.

Still another property desired for the electrode support substrate isthat the shape property of the support substrate itself is improved sothat burrs, projections, undulations and others, which becomestress-concentrated spots when they receive stacking-load or thermalshock, are made as small as possible. This is based on the followingreason. As described above, the electrode support substrate is requiredto have an appropriate electrical conductivity. Further, the substratemust be a porous substrate having pores sufficient for allowing a fuelgas and others to permeate and diffuse through the substrate; thus,numerous openings are present in the surface thereof. Therefore, inorder to restrain the support substrate, even admitting that thesubstrate is such a porous sheet, from being cracked or damaged by localstress concentration caused when it receives stacking-load, it isnecessary to restrain the generation of burrs, which are formed at itsinternal and external circumferential edges at the time of punching, andprojections or undulations, which may be formed inside the substrate, asmuch as possible. Furthermore, the electrode support substrate which isintended in the present invention must be a porous body through which agas can permeate and diffuse. Therefore, the shape property effectivefor the printability of a dense sheet, such as a solid electrolyte film,and effective for the prevention of stress concentration thereon cannotbe applied, as it is, to the electrode support substrate.

The present invention has been made, paying attention to a situation asdescribed above. An object thereof is to provide an electrode supportsubstrate to which electrode or a solid electrolyte film may be appliedby screen printing. The substrate has the following characteristics. Theentire surface of the substrate is stable against a fuel gas and others;the substrate has superior gas permeability/diffusibility. The substrateis able to form a printed electrode and a solid electrolyte film thatare even and closely adhesive. The substrate has such a shape propertythat even if a plurality of the substrates are laminated into a cellstack and each of the substrates receives a large stacking-load, thesubstrate is not easily cracked or damaged by local stressconcentration.

DISCLOSURE OF THE INVENTION

The subject matter of the electrode support substrate of the presentinvention for a fuel cell, which has solved the above-mentionedproblems, is that the substrate comprises a ceramic sheet having aporosity of 20 to 50%, a thickness of 0.2 to 3 mm and a surface area of50 cm² or more, and the variation coefficient of measured values of thegas permeable amounts of any area of 4 cm² selected optionally from thewhole of the surface area of substrate, the values being measured by themethod according to JIS K 6400, is from 5 to 20%.

The electrode support substrate of the present invention for a fuel cellpreferably satisfies the following as a requirement for obtainingsuperior adhesion and evenness when an anodic electrode and so on areprinted and formed on the surface of substrate, as well as theabove-mentioned requirement: the surface roughness measured with a laseroptical manner three-dimensional shape measuring device is 1.0 to 40 μmas the maximum roughness depth (Rmax: German Standard “DIN 4768”)thereof.

Furthermore, the electrode support substrate of the present inventionfor a solid oxide type fuel cell is used in a multi-layered andlaminated state, as described above; therefore, in order to suppresscracking or breaking based on stacking-load as much as possible when thesubstrate is used, it is desired that height of burrs measured with thelaser optical manner three-dimensional shape measuring device is ½ orless of the thickness of the sheet. Further, it is desired that largestheight(s) of undulations and/or projections measured with the same laseroptical manner three-dimensional shape measuring device is/are ⅓ or lessof the thickness of the sheet.

The producing process of the present invention is placed as a producingprocess making it possible to obtain surely an electrode supportsubstrate for a fuel cell, in particular, an electrode support substratefor a fuel cell which satisfies the above-mentioned properties. Aboveprocess has a feature in: using, as a slurry for producing a green sheetwhich becomes a ceramic precursor, a slurry which comprises anconductive component powder, an skeleton component powder, apore-forming agent powder, and a binder, defoamed under reduced pressureafter milling to adjust the viscosity thereof to 40 to 100 poise (25°C.), and kept at room temperature while rotating stirring fans thereinat a rotating speed of 5 to 30 rpm for 20 to 50 hours; fashioning theslurry into a sheet by a doctor blade method to obtain a green sheet;cutting the green sheet into a given shape; and then firing the greensheet having the given shape.

When the producing process is carried out, it is desired to use, as theslurry for producing the green sheet, a slurry wherein its particle sizedistribution has a peak in each of ranges of 0.2 to 2 μm and 3 to 50 μmand the content ratio by mass of fine particles in the range of 0.2 to 2μm to coarse particles in the range of 3 to 50 μm is in a range of 20/80to 90/10. Further, it is preferred to use a slurry containing 5 to 30parts by mass of the binder and 2 to 40 parts by mass of thepore-forming agent powder with respect to 100 parts by mass of the totalof the conductive component powder and the skeleton component powder.

In order to obtain the electrode support substrate satisfying theabove-mentioned preferred height of burr and preferred height ofundulation and/or projection, which is intended in the presentinvention, it is desired that when the green sheet is punched into ashape used as product, a punching blade having a waver-form blade edgeis used. It is more preferred to use the punching blade which the angle(α₁), (α₂), (θ₁) and (θ₂) thereof satisfy the following relationship:α₁=30 to 120°, 20°≦α₂=θ₁+θ₂≦70°, and θ₁≦θ₂,

-   the angle (α₁) meaning of angle being viewed from the side face of    the wave-form blade,-   the angle (α₂) meaning of blade edge angle of the cross section of    the blade,-   the angle (θ₁) meaning of angle made between the surface thereof on    the side of the sheet becoming a product and a center line (x)    passing through the blade edge,-   the angle (θ₂) meaning of angle made between the surface thereof on    the side of the rest of the sheet and the center line (x) passing    through the blade edge. According to this, height of undulations    and/or projections and/or burrs can be favorably suppressed into as    low a value as possible.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a frequency graph illustrating a preferred particle sizedistribution of a slurry, for producing a green body, which ispreferably used upon producing an electrode support substrate for a fuelcell according to the present invention;

FIG. 2 is an explanatory sectional view illustrating the shape of a burrformed on an electrode substrate, which is measured with a laser opticalmanner three-dimensional shape measuring device;

FIG. 3 is an explanatory enlarged view illustrating a projection whichmay be generated in the surface of an electrode substrate, which ismeasured with a laser optical manner three-dimensional shape measuringdevice; and

FIG. 4 is an explanatory view illustrating an undulation which may begenerated in the whole of an electrode substrate, which is measured witha laser optical manner three-dimensional shape measuring device.

FIG. 5 is a view showing an example of the particle size distribution ofa slurry which is preferably used upon producing a green body whichbecomes a precursor of an electrode substrate according to the presentinvention;

FIG. 6 is an explanatory side view illustrating the blade edge shape ofa preferred punching blade used to punch a green sheet upon producing anelectrode substrate for a fuel cell according to the present invention;

FIG. 7 is an explanatory sectional view illustrating the blade edgeshape of a preferred punching blade used to punch a green sheet uponproducing an electrode substrate for a fuel cell according to thepresent invention;

FIG. 8 is an explanatory sectional view illustrating a preferred exampleexpect FIG. 7 of a punching blade used in the present invention;

FIG. 9 is an explanatory schematic sectional view showing the structureof a punching machine adopted preferably in the present invention and apunching work example;

FIG. 10 is an explanatory schematic sectional view showing the structureof the punching machine adopted preferably in the present invention andthe punching work example;

FIG. 11 is an explanatory schematic sectional view showing the structureof the punching machine adopted preferably in the present invention andthe punching work example; and

FIG. 12 is an explanatory view showing an outline of a gas permeationresistance measuring device used in examples of the present invention.

1: blade edge portion, h: height of blade, p: pitch of blade edge, t:thickness of blade, and α₁, α₂, θ₁ and θ₂: angle of blade edge

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors have been advancing research for providing anelectrode support substrate which can surely obtain a printed electrodethat is particularly dense, even and closely adhesive while gaspermeability/diffusibility necessary for a practical electrode supportsubstrate is kept under the above-mentioned themes to be solved.

As a result, it has been found out that a ceramic sheet having aporosity of 20 to 50%, a thickness of 0.2 to 3 mm and a surface area of50 cm² or more, as a ceramic constituting a substrate. The substratesatisfies the following: the variation coefficient of measured values ofthe gas permeable amounts of any areas of 4 cm² selected optionally fromthe whole of the surface area, the values being measured by the methodaccording to JIS K 6400, is from 5 to 20% is substantially even in thestate of pore distribution throughout the substrate for supporting anelectrode, and can exhibit stable and superior gaspermeability/diffusibility.

The electrode support substrate of the present invention is essentiallya porous substrate having electrical conductivity, superior thermalshock resistance and mechanical strength and further having sufficientgas permeability/diffusibility, as described above. The specificstructure of the electrode support substrate which can satisfy theserequirements will be described in detail hereinafter.

The electrode support substrate comprises, as main constitutingmaterials, a conductive component for giving electrical conductivity,and a ceramic material which becomes a skeleton component of asubstrate. The conductive component is a component essential for givingelectrical conductivity to the substrate. Examples of the componentwhich becomes a component of an anodic electrode support substrateinclude metals oxides which are changed to conductive metals underreducing atmosphere when the fuel cell operates, such as iron oxide,nickel oxide and cobalt oxide; metal oxides which exhibit electricalconductivity in reducing atmosphere, such as ceria, yttria-doped ceria,samaria-doped ceria, prasea-doped ceria, and gadolia-doped ceria; andnoble metals which exhibit electrical conductivity, such as platinum,palladium, and ruthenium. These may be used alone, or may be used incombination of two or more which are appropriately selected therefrom ifnecessary. Of these conductive components, nickel oxide has the highestwide-usability, considering cost or electrical conductivecharacteristics.

The skeleton component is a component important for keeping strengthnecessary for an electrode support substrate, in particular, strengthwhich resists thermal shock and stacking-load and further important forrelieving difference in thermal expansion from the solid electrolyte. Inthe case that the solid electrolyte is zirconia, a single material or acomposite material from zirconia, alumina, magnesia, titania, aluminumnitride, mullite and others are used. Of these, stabilized zirconia hasthe highest wide-usability. Preferred examples of the stabilizedzirconia include solid solutions obtained by dissolving, into zirconia,one or more oxides selected from the following as a stabilizer orstabilizers: oxides of alkaline earth metals, such as MgO, CaO, SrO andBaO; oxides of rear earth elements, such as Y₂O₃, La₂O₃, CeO₂, Pr₂O₃,Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃; andSc₂O₃, Bi₂O₃, and In₂O₃. Additional preferred examples includedispersion strengthened zirconia wherein a dispersing strengtheningagent such as alumina, titania, Ta₂O₅ or Nb₂O₅ is added to theabove-mentioned solid solutions.

There can also be used a ceria based or bismuth based ceramic whereinone or more of the following are added to CeO₂ or Bi₂O₃: CaO, SrO, BaO,Y₂O₃, La₂O₃, Ce₂O₃, Pr₂O₃, Nb₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dr₂O₃,Ho₂O₃, Er₂O₃, Yb₂O₃, PbO, WO₃, MoO₃, V₂O₅, Ta₂O₅ and Nb₂O₅; or a gallatebased ceramic such as LaGaO₃.

Of these, particularly preferable are zirconia stabilized with 2.5 to12% by mole of yttria, or zirconia stabilized with 3 to 15% by mole ofscandia.

The content blend between the conductive component and the skeletoncomponent is important for giving appropriate electrical conductivityand strength property to the resultant electrode support substrate. Whenthe amount of the conductive component becomes relatively large, theelectrical conductivity of the substrate is improved but the strengthproperty lowers since the amount of the skeleton component becomesrelatively small. Conversely, when the amount of the conductivecomponent becomes relatively small, the strength property becomes highbecause of an increase in the amount of the skeleton component. Thus,the blend ratio between the two should be appropriately decided underthe consideration of the balance between the above-mentioned matters.The ratio is changed on the basis of the kind of the conductivecomponent, and others, but it is preferable in the present invention,which mainly aims at an anodic electrode support substrate, that theratio of the skeleton component amount to the conductive componentamount is in the range of 60-20 to 40-80% by mass, more generally 50-30to 50-70% by mass.

The electrode support substrate of the present invention comprises aconductive component and a skeleton component, as described above. Themechanical strength and thermal stress resistance thereof are kept bythe skeleton component, and electrical conductivity is given to thesubstrate by the conductive component. The electrode support substrate,which is made of them, needs to have pores through which a fuel gas or aburning exhaust gas permeates or diffuses, as described above. In orderto pass these gases smoothly under low pressure loss, it isindispensable that the substrate has a porosity of 20% or more as awhole under oxidizing atmosphere. If the porosity is less than 20%, thegases permeate or diffuse insufficiently so that the efficiency of powergeneration falls. The porosity is more preferably 25% or more, even morepreferably 30% or more.

However, if the porosity is too large, the strength property and thermalstress resistance of the substrate lower so that the followingtendencies are generated: when the substrate is integrated into a stack,the substrate is easily cracked or deteriorated by staking-load, thermalshock or the like; or the distribution state of the conductive componentbecomes thin so that the substrate has an insufficient electricalconductivity. Therefore, it is advisable that the porosity is restrainedinto 50% or less at highest, preferably 45% or less, more preferably 40%or less.

It is indispensable that the thickness of the electrode supportsubstrate of the present invention is in the range of 0.2 to 3 mm. Ifthe thickness is less than 0.2 mm, the substrate is too thin so that thesubstrate does not easily keep strength for a practical electrodesupport substrate. On the other hand, if the substrate is madeexcessively thick to make the thickness into more than 3 mm, thestrength is improved but when a large number of the electrode supportsubstrates are laminated to be made practicable as a cell stack, thewhole of the laminated structure becomes thick. The structure is noteasily suitable for a desire that the structure is made compact as apower generator. When the electrode support substrate is madepracticable as a substrate for a fuel cell, the thickness thereof ismore preferably 0.3 mm or more and 2 mm or less.

The size of the electrode support substrate according to the presentinvention, which depends on the use purpose or scale thereof, isimportant for ensuring electric power generation at a level satisfactoryfor practical use. For this purpose, the substrate should ensure anecessary and minimum surface area. It is desired that the substrateensures a sheet area (surface area on a single side thereof) of 50 cm²or more, more preferably 100 cm² or more.

It is essential that the electrode support substrate satisfies thefollowing: under the conditions that the above-mentioned porosity,thickness and surface area are satisfied, the above-mentioned variationcoefficient of the measured values of the gas permeable amounts of anyplural areas of 4 cm² selected optionally from the whole of the surfacearea of the substrate ranges from 5 to 20%, and the substrate exhibitssubstantially even gas permeability/diffusibility as a whole.

In order to pass a fuel gas or a reaction-produced gas rapidly into theelectrode support substrate, it is naturally preferred that the whole ofthe substrate has even gas permeability/diffusibility as a whole. Forthis purpose, it is desired that the distribution state of poresthroughout the substrate is even.

However, only by measuring the porosity of the whole, it is impossibleto specify whether the pores are pores continuing to the inside of thesubstrate or pores which are closed inside the substrate. Thus, theporosity may be insufficient as information on permeability.

Permeability is an important factor as a physical property of anyelectrode support substrate. The permeability thereof has beenrepeatedly investigated, so as to find out: when the gas permeableamounts of any specified areas in the entire surface area of a substratefluctuate, a fuel gas is unevenly distributed in the entire surface ofthe substrate to generate locally regions where electric powergeneration is large and regions where electric power generation issmall, so that a temperature distribution is generated to cause thegeneration of a crack in the substrate; and the specification of thefluctuation causes the electrode support substrate to exhibit excellentproperty for a practical electrode support substrate.

The size of any electrode support substrate for a solid oxide type fuelcell is expected to be from about 50 to 1000 cm², more generally about100 to 500 cm² for practical use. Therefore, a standard for checking theevenness of the distribution state of pores throughout the substrate hasbeen defined as 4 cm², which is {fraction (1/10)} or less of the minimumarea 50 cm² of the substrate, considering the minimum area. In the casethat the area to be measured is made smaller, the distribution state ofthe pores throughout the substrate can be observed. Thus, this case ispreferred. However, even if an area having each side of 1.5 cm length(area: 2.25 cm²) was measured, a significant different between themeasurement results and the measurement results about 4 cm² was notrecognized. In the measurement of the gas permeability distribution, itis preferable that at least five spots are selected optionally from theentire surface of a supplied substrate and then the gas permeableamounts thereof are measured. In the present invention, the variationcoefficient of measured values of the gas permeable amounts obtained bythis method is specified as 5 to 20%.

Any one of the gas permeable amounts is a value measured according togas permeable amount measuring method of JIS K 6400 (1997) about softurethane foam testing methods. Specifically, a stationary flowdifferential pressure measuring method is adopted which comprisescutting a substrate into a piece 3 cm square (area: 9 cm²) with adiamond cutter, reducing the pressure on a single surface side (lowpressure side) of this test piece, introducing air onto the othersurface side thereof, and measuring the gas permeable amount by anincrease in the pressure on the low pressure side. Both ends of the testpiece are used by 0.5 cm, respectively, to hold the test piece, therebyyielding an effective gas permeable area of 4 cm². As the resultant gaspermeable amount data of the supplied substrate, the variationcoefficient is used which is obtained by obtaining the standarddeviation for representing the fluctuation or scattering of measuredvalues of the gas permeable amount relatively, and then dividing it bythe average thereof.

In the present invention, the variation coefficient is specified as 5 to20%, more preferably 5 to 15%, even more preferably 5 to 13%. Forreference, if the variation coefficient exceeds 20%, the substrate iscracked or broken in almost all cases. It appears that this is based onthe following reason: when a fuel gas permeates through the inside ofthe substrate, the gas cannot pass evenly to be unevenly distributed sothat the fuel gas reaching the vicinity of the electrolyte becomesuneven dependently on spots; consequently, regions where electric powergeneration is large and regions where this is small can be locallygenerated so that a temperature distribution is generated.

If the gas permeable amount in the substrate is completely constant overthe entire surface thereof, the variation coefficient is 0%. However,the variation coefficient obtained by the above-mentioned method is 5%at lowest; therefore, this is decided as the lower limit for practicaluse.

In the present invention, it is desired that the distribution state ofthe pores throughout the substrate is even and further it is preferablethat the size of the pores is 3 μm or more and 20 μm or less as theaverage diameter thereof. If the average diameter of the pores is lessthan 3 μm, the gas permeability/diffusibility are insufficient so thatthe same problems as in the case that the porosity is insufficient maybe caused. Conversely, if the average diameter is too large, thestrength tends to deteriorate and the electrical conductivity tends tobe insufficient in the same manner as in the case that the porosity isexcessive. Therefore, it is preferable to suppress the diameter into 20μm or less.

The porosity of the substrate, the variation coefficient of measuredvalues of the gas permeable amounts, and the preferable average diameterof the pores can be adjusted by the kind and the blend amount of apore-forming agent used when the substrate is produced, the particlesize construction of starting material powder, the temperature at thetime of firing a green sheet which will become a substrate precursor,and others. Specific methods thereof will be described later.

As described, an anodic electrode or an electrolyte layer is formed on asingle surface of the electrode support substrate of the presentinvention by screen printing or the like. In order to make the electrodeor electrolyte printing even and sure with close adhesion, it isnecessary to control the surface thereof into an appropriate surfaceroughness. The present inventors have made it evident by experimentsthat the maximum roughness depth (Rmax: German Standard “DIN 4768”)thereof is set to 1.0 μm or more and 40 μm or less. Furthermore, in theelectrode support substrate of the invention, which is porous in orderto ensure the gas permeability/diffusibility thereof, whether thesurface property is good or bad cannot be precisely estimated accordingto the surface roughness obtained by using a contact type surfaceroughness meter which is generally adopted for dense sheets. Thus, it isdesired that the surface is made to satisfy the above-mentioned Rmax onthe basis of the surface roughness measured with a laser optical mannerthree-dimensional shape measuring device.

If the Rmax is less than 1.0 μm, the surface is too smooth so that theelectrode printing tends to be insufficient in close adhesion. Thus, itis feared that the printed electrode layer is peeled from the substrateby thermal shock receiving when the fuel cell is handled or operated.Additionally, the gas permeability/diffusibility tend to turninsufficient. On the other hand, if the Rmax exceeds 40 μm, thethickness of the electrode layer becomes uneven when the electrode isprinted, or a part of the electrode-constituting material is embedded inconcave portions in the surface. Thus irregularities are formed in theelectrode layer surface to result in an increase in electric conductanceloss. Furthermore, a crack may be generated in the electrode layer whenthe electrode-constituting material is fired or the resultant cell isused as a fuel cell. In order to decrease the electric conductance lossas much as possible and heighten the close adhesion of the printedelectrode layer, the Rmax is more preferably 0.2 μm or more and 30 μm orless, even more preferably 20 μm or less.

The reason why the laser optical manner three-dimensional shapemeasuring device, which is of a non-contact type, is used in the presentinvention to evaluate the surface roughness is based on the following.In the case of the electrode support substrate of the invention, whichis porous and has a surface on which innumerable pores are opened, thesurface roughness is not smoothly and easy measured with any surfaceroughness meter of a contact type, such as a stylus type, since thestylus is caught by the pores; moreover, the surface roughness cannot beprecisely measured in the contact manner since the pores opened in thesurface are relatively deep.

At any rate, in the present invention, the variation coefficient ofmeasured values of the gas permeable amounts, which is obtained by theabove-mentioned method, is from 5 to 20%, and further the maximumroughness depth (Rmax) is preferably made into an appropriate range.Thereby make it possible to print an electrode on surface of substrate,substrate is porous and have even in thickness, which has even gaspermeability/diffusibility in the entire surface thereof not to causeany uneven gas flow or any extreme temperature distribution when theelectrode is operated, and which has a highly close adhesion. In orderto ensure such evenness of the gas permeability/diffusibility and anappropriate surface roughness, it is necessary to control properly theparticle size construction of starting material powder used to produce agreen sheet which will become a precursor of the ceramic whichconstitutes the electrode support substrate, conditions for producing orfiring the green sheet, and others. These will be described later.

Since a large number of the electrode support substrates of theinvention are laminated in the upper and lower directions so as to beintegrated into a stack as described above, the stack is subjected to alarge stacking-load and further receives thermal shock or thermal stressbased on heat generated when the stack is operated. Therefore, even if aslight number of burrs or projections are present on the laminationfaces, stress is concentrated on the portions thereof so that crackingor breaking may be caused. When such cracking or breaking is generatedin the substrates, the cracking spreads to the anodic electrodes andothers formed on the surfaces so that the electrical conductivitythereof is blocked. If the cracking or breaking spreads to the solidelectrolyte film, the effect of shielding the fuel gas and others islost so that the stack comes not to act as a fuel cell. If the burrs,projections or undulations on the substrate surface(s) become large, theanodic layers and the solid electrolyte layer(s) formed on the surfacesbecome uneven and further the adhesion of the layers to the substratesbecomes poor. It is therefore desired that the burrs generated to thecircumferential edges of the substrates are made as small as possibleand further the projections or undulations on the substrate surfaces arepreferably made as small as possible, thereby restraining local stressconcentration generated in the lamination state into as small a value aspossible.

The present inventors has made it evident by experiments that: asubstrate sheet wherein height of burrs in the circumferential edgethereof, measured with a laser optical manner three-dimensional shapemeasuring device, is ½ or less of the thickness of the sheet, the heightof the largest projection measured with the same laser optical mannerthree-dimensional shape, measuring device, is preferably ⅓ or less ofthe sheet thickness, and the height of the largest undulation, measuredwith the same laser optical manner three-dimensional shape measuringdevice, is ⅓ or less of the sheet thickness. The substrate sheet exhibitstable and have superior resistance against stacking-load, thermal shockresistance, and thermal stress resistance. Further the substrate sheetcan have superior performance about printing adaptability when anelectrode is formed or a solid electrolyte film is formed thereon.

If the height of the burrs in the substrate circumferential edge exceeds½ of the sheet thickness, at the time of using this substrate as oneelement and integrating the substrate into a stack, stress based onintegrating force or stacking-load is concentrated onto the large burr.Consequently, before the stack is operated as a fuel cell, the substrateis broken or cracked together with the electrode layers or solidelectrolyte films thereon. Alternatively, the stress-concentratedportions are cracked or broken by receiving thermal hysteresis when thestack is operated even if cracks and others are not generated at thetime of the integration. Thus, the power generation performance of thefuel cell is remarkably decreased. However, it has been made evidentthat: a substrate wherein the burr height is ½ or less of the sheetthickness, more preferably ⅓ or less thereof, even more preferably ¼ orless thereof is hardly cracked or broken even if the substrate receivesstacking-load or thermal stress at a practical level; and this substratecan use as substrate for a fuel cell which can maintain a givenpower-generating performance for a long term.

The burr height in the present invention means the difference betweenthe highest portion and the lowest portion in a section in aperpendicular line direction from the external circumferential (orinternal circumferential) edge of a cut face of a substrate, and can beobtained with a laser optical manner three-dimensional shape measuringdevice, which is of a non-contact type, as illustrated, for example, inFIG. 1.

At any rate, when the burr height obtained by the above-mentioned methodis restrained into ½ or less of the sheet thickness in the presentinvention, local stress concentration based on load or thermal shock inthe laminated state is suppressed into a minimum so that the generationof cracking or breaking can be suppressed into a minimum. In order toobtain such a surface roughness, it is important to contrive a bladeshape when a green sheet which becomes a ceramic precursor constitutingthe electrode substrate is subjected to punching work. This will bedescribed later.

In the present invention, it is desired to make the height of thelargest projection or the largest undulation on the substrate surface,besides the burr height, as small as possible. The standard thereof isas follows: in order to restrain stress concentration when stacking-loadis received and restrain cracking or breaking similarly and further makeeven an electrode layer or a solid electrolyte film formed on theelectrode surface, the largest projection height, measured with the samelaser optical manner three-dimensional shape measuring device, isdesirably set to ⅓ or less of the sheet thickness, more preferably ¼ orless thereof, even more preferably ⅕ or less thereof and the largestundulation height is desirably set to ⅓ or less of the sheet thickness,more preferably ¼ or less thereof, even more preferably ⅕ or less.

The projections mean convex portions which are basically independentlygenerated on the surface of the electrode sheet and have a diameter ofabout 2 to 15 mm (more generally 5 to 10 mm), for example, asillustrated in FIG. 2, and the undulations mean distortion which iseasily generated on the electrode sheet, in particular, acircumferential edge portion thereof and which is continuous into a waveform, for example, as illustrated in FIG. 3. These can be obtained byradiating a laser ray onto the surface of the sheet and analyzing thelight reflected thereon three-dimensionally.

The shape of the ceramic sheet which constitutes the electrode supportsubstrate of the present invention may be any shape, such as a circle,ellipse, rectangle, or rectangle having a roundish corner, and may be ashape wherein such a sheet has therein one or more holes which have ashape of a similar circle, ellipse, rectangle or rectangle having aroundish corner, or some other shape. The area of the sheet is notparticularly limited, and is generally 50 cm² or more, more preferably100 cm² or more, even more preferably 200 cm² or more under theconsideration of practical use. When the holes are present in the sheet,this area means the total area including the area of the holes.

The following describes a process for producing an electrode supportsubstrate according to the present invention.

About the electrode support substrate of the present invention, a powdermade of a metal or metal oxide which becomes the above-mentionedconductive component, a metal oxide powder which becomes the skeletoncomponent, and a pore-forming agent powder blended for making pores arehomogeneously mixed with an organic or inorganic binder, a dispersingmedium (solvent), an optional dispersing agent, an optional plasticizerand others in the same method as described above, so as to prepare apaste. The resultant paste is applied onto a flat and smooth sheet (suchas a polyester sheet) by any method such as a doctor blade method, acalendar roll method or an extruding method, so as to have anappropriate thickness. The resultant is dried to volatilize and removethe dispersing medium (solvent), thereby yielding a green sheet.

The pore-forming agent used herein may be an agent of any kind if theagent is burned up under the above-mentioned firing conditions. Thefollowing is used: a natural organic powder such as wheal powder, cornstarch, sweet potato powder, potato powder or tapioca powder, acrosslinked fine particle aggregate made of (meth)acrylic resin or thelike, a thermally-decomposing or sublimating resin powder of melaminecyanurate, or a carbonous powder such as carbon black or activatedcarbon Of these, preferable are corn starch, the acrylic crosslinkedfine particle aggregate, carbon black and so on since they can carry andcontain a large amount of the conductive component as described later.

The shape of these pore-forming agent powders is desirably a sphericalshape or a rugby ball shape in order to cause a large amount of theconductive component to be carried and contained therein and promote aneven distribution of the conductive component into the ceramic substrateobtained by firing. Preferably, the powder or fine particle aggregateitself has pores or capillaries so as to cause the conductive componentto be contained in the powder or the fine particle aggregate.

A preferable particle size of the powder or the crosslinked fineparticle aggregate which become the pore-forming agent is 0.5 to 100 μm,more preferably 3 to 50 μm as the average particle size thereof measuredwith a laser diffraction type particle size distribution meter (tradename: “SALD-1100”, manufactured by Shimadzu Corp.), and is 0.1 to 10 μm,more preferably 1 to 5 μm as the 10% by volume diameter thereof.

Particularly preferable is a fine particle aggregate of 0.5 to 100 μmaverage particle size, wherein crosslinked polymer fine particles of0.01 to 30 μm average particle size aggregate with each other, the fineparticle aggregate being obtained by emulsion-polymerizing a(meth)acrylic monomer, as disclosed in, for example, JP-A 2000-53720.

In the present invention, the pore-forming agent may be mixed with eachof the above-mentioned starting powders to prepare slurries for formingthe green sheet. It is however effective to mix or compound thepore-forming agent and the above-mentioned conductive component andsubsequently mix the resultant with the other staring materials. Thatis, the following method can be adopted:

-   -   (1) a method of blending the conductive component powder or a        precursor compound thereof with the pore-forming agent at a        given ratio, and wet-mixing or dry-mixing the blended        components, thereby sticking the conductive powder or the        precursor compound evenly onto the surface of the pore-forming        powder,    -   (2) a method of sticking the conductive component powder or a        precursor compound evenly onto the surface of the pore-forming        agent by a spray method or the like, and    -   (3) a method of incorporating the conductive component powder or        a precursor compound thereof into pores or gaps in a fine        particle aggregate for forming pores.

More specifically, it is possible to modify a method as disclosed inJP-A 07-22032 (1995) and adopt a method of mixing the pore-forming agentpowder with a precursor compound which can generate an conductivecomponent by thermal decomposition, and volatilizing the solvent whiledry-pulverizing the mixture in a mill or the like, or volatilizing thesolvent while wet-pulverizing the mixture, or some other method.

It is preferable to adopt a method as disclosed in JP-A 2000-53720 orJP-A 2001-81263 or some other method. It is emulsion-polymerized a(meth)acrylic polymerizable monomer mixture to produce a fine particleaggregate of 0.5 to 100 μm average particle size wherein crosslinkedpolymer fine particles of 0.01 to 30 μm average particle size adhere toeach other. The fine particle aggregate mix with a precursor compoundwhich can generate an conductive component by thermal decomposition,causing these to enter gaps in the fine particle aggregate, and thendrying the resultant to volatilize and remove the solvent.

When the pore-forming agent into which the conductive component isincorporated is used in this way, the following advantageous effects canbe obtained: the pore-forming agent is burned up when the green sheet isfired, so that pores are made in the portions thereof when theconductive component is also present in the portions, the pores arepresent near the conductive component after the firing; and even if theconductive component is oxidized to undergo volume expansion at the timeof making the substrate practicable as an electrode support substratefor a fuel cell, the above-mentioned pore portions absorb straingenerated by the volume expansion so that the generation of breaking orcracking, which may easily be caused in the electrode support substrate,is prevented. As a result, in particular, the thermal shock resistanceand the thermal stress resistance of the electrode support substrate canbe made high.

The pore-forming agent is an important component, which is burned up atthe time of the heating and firing as described above so as to give gaspermeability/diffusibility to the electrode support substrate. In orderto ensure a porosity of 20% or more and 50% or less, which is desiredfor the porous body in the present invention, it is desired that theblend amount of the pore-forming agent is set to 2 parts or more and 40parts or less, more preferably 5 parts or more and 30 parts or less bymass for 100 parts by mass of the total of the conductive componentpowder and the skeleton component powder. If the blend amount of thepore-forming agent is insufficient, pores made by thermal decompositionwhen the green sheet is heated and fired tend to be short so that anelectrode support substrate having satisfactory gaspermeability/diffusibility is not easily obtained. Conversely, if theblend amount of the pore-forming agent is too large, the number of thepores made at the time of the heating and firing becomes excessivelylarge so that the sintered product becomes sufficient in strength andfurther a flat substrate is not easily obtained. In this case, it ispossible to advance the sintering and lower the porosity by making thesintering temperature high or extending the sintering time. However,this is not economical since a long time is required for the sinteringand further energy consumption also increases to a large extent.

The kind of the binder used in the production of the green sheet is notparticularly limited, and a binder selected appropriately from organicbinders which have been known hitherto can be used. Examples of theorganic binders include ethylene type copolymer, styrene type copolymer,acrylate or methacrylate type copolymer, vinyl acetate type copolymer,maleic acid type copolymer, vinyl butyral type resin, vinyl alcohol typeresin, waxes, and ethyl celluloses.

Of these, the following examples are given from the viewpoints of theformability into a green sheet, punchability, strength, thermaldecomposability when they are fired, and others: polymers obtained bypolymerizing or copolymerizing at least one of alkyl acrylates having analkyl group having 10 or less carbon atoms, such as methyl acrylate,ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate,cyclohexyl acrylate, and 2-ethylhexyl acrylate; alkyl methacrylateshaving an alkyl group having 20 or less carbon atoms, such as methylmethacrylate, ethyl methacrylate, butyl methacrylate, isobutylmethacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decylmethacrylate, dodecyl methacrylate, lauryl methacrylate, and cyclohexylmethacrylate; acrylates or methacrylates having a hydroxyalkyl group,such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxymethacrylate, and hydroxypropyl methacrylate; aminoalkyl acrylates oraminoalkyl methacrylates, such as dimethylaminoethyl acrylate, anddimethylaminoethyl methacrylate; carboxyl-containing monomers, such asacrylic acid, methacrylic acid, maleic acid, and monoisopropyl maleate.These may be used alone. Alternatively, if necessary, these may be usedin an appropriate combination of two or more thereof.

Of these, particularly preferable are acrylate or methacrylate typecopolymers having a number-average molecular weight of 5,000 to 200,000,more preferably 10,000 to 100,000. Of these, the following isrecommendable as preferred one: copolymer comprising, as a monomercomponent, isobutyl methacrylate and/or 2-ethylhexyl methacrylate in anamount of 60% or more by mass.

About the use ratio between the starting powders (the total of theconductive component, the skeleton component, and the pore-formingagent) and the binder, the amount of the latter is 5 parts or more and30 parts or less, more preferably 10 parts or more and 20 parts or lessby mass for 100 parts by mass of the former. If the used amount of thebinder is short, the strength or the flexibility of the green sheetbecomes insufficient. Conversely, if the amount is too large, theviscosity of the slurry is not easily adjusted and further the bindercomponent is actively decomposed or released into a large amount whenthe green sheet is fired. Thus, the surface property of the green sheetdoes not become even with ease.

As the dispersing medium used in the production of the green sheet, thefollowing is appropriately selected and used: an alcohols such asmethanol, ethanol, 2-propanol, 1-butanol, 1-hexanol or 1-hexanol; aketone such as acetone or 2-butanone; an aliphatic hydrocarbons such aspentane, hexane, or heptane; an aromatic hydrocarbons such as benzene,toluene, xylene, or ethylbenzene; an acetates such as methyl acetate,ethyl acetate, or butyl acetate; or the like. These dispersing mediummay be used alone. Alternatively, if necessary, these may be used in anappropriate combination of two or more thereof. The most ordinary onesof these dispersing medium are 2-propanol, toluene, ethyl acetate and soon.

In the preparation of the slurry for producing the green sheet, thepore-forming agent powder into which the above-mentioned conductivecomponent powder or a precursor compound thereof is incorporated, theskeleton powder, and an conductive component powder which may beoptionally replenished are homogeneously mixed with the binder, thedispersing medium, an optional dispersing agent for promoting thedissociation or dispersion of the starting powders, an optionalplasticizer and others, so as to prepare the slurry in a homogeneousdispersion state.

As the dispersing agent used therein, the following is used: a polymerelectrolyte such as polyacrylic acid or polyacrylic ammonium; an organicacid such as citric acid or tartaric acid; a copolymer made fromisobutylene and styrene or maleic anhydride, or an ammonium salt oramine salt thereof; a copolymer made from butadiene and maleicanhydride. The plasticizer has an effect of making the flexibility ofthe green sheet high, and specific examples thereof include phthalatessuch as dibutyl phthalate and dioctyl phthalate; and glycols such aspropylene glycol and glycol esters.

The starting powder which becomes the skeleton of the electrode supportsubstrate according to the invention is preferably one wherein theaverage particle size is 0.1 μm or more and 3 μm or less and theparticle size of the 90% volume thereof is 6 μm or less; more preferablyone wherein the average particle size is 0.1 μm or more and 1.5 μm orless and the particle size of the 90% volume is 3 μm or less; and evenmore preferably one wherein the average particle size is 0.2 μm or moreand 1 μm or less and the particle size of the 90% volume is 2 μm orless. The powder used as the starting material of the conductivecomponent is preferably one wherein the average particle size is 0.6 μmor more and 15 μm or less and the particle size of the 90% volume is 30μm or less; more preferably one wherein the average particle size is 0.6μm or more and 3 μm or less and the particle size of the 90% volume is20 μm or less; and even more preferably one wherein the average particlesize is 0.6 μm or more and 1.5 μm or less and the particle size of the90% volume is 10 μm or less. In particular, in the case that nickeloxide powder is used as the constituent material of the conductivecomponent, it is preferable to use a powder wherein the particle size ofthe 90% volume is 6 μm or less, more preferably 3 μm or less and theamount of contained coarse particles is made as small as possible.

In the case that a powder wherein the average particle size exceeds 3 μmand the particle size of the 90% volume exceeds 6 μm is used as thestarting powder which constitutes the skeleton component and further apowder wherein the average particle size exceeds 15 μm and the particlesize of the 90% volume exceeds 30 μm is used as the starting powderwhich becomes the constituent material of the conductive component,desired thermal shock resistance and mechanical strength are not easilyobtained since the green sheet is pre-fired to be made porous andfurther gaps between the particles become pores. On the other hand, inthe case that a powder wherein the average particle size is less than0.1 μm is used as the constituent material of the skeleton component andfurther a powder wherein the average particle size is less than 0.6 μmis used as the constituent material of the conductive component, poresin the sintered body becomes too small even if the pore-forming agent isused together. As a result, the gas permeability/diffusibility thereofis liable to become insufficient.

However, in order to obtain surely an electrode support substratesatisfying an appropriate surface roughness, that is, the requirementthat the maximum roughness depth (Rmax) is 1.0 μm or more and 40 μm orless as the surface roughness measured with a laser optical mannerthree-dimensional shape measuring device while the variation coefficientof measured values of the gas permeable amounts is kept into the rangeof 5 to 20%, which is the most important in the invention, it is desiredto adopt a process of:

-   -   using a slurry for producing of green sheet becoming a ceramic        precursor, including an conductive component powder, an skeleton        component powder, a pore-forming agent powder and a binder,        defoamed under reduced pressure after milling to adjust the        viscosity thereof to 40 to 100 poise (25° C.), and kept at room        temperature while rotating stirring fans therein at a rotating        speed of 5 to 30 rpm for 20 to 50 hours;    -   fashioning the slurry into a sheet by a doctor blade method to        obtain a green sheet;    -   cutting the green sheet into a given shape; and        then firing the green sheet having the given shape.

This is based on the following reason. When this process is adopted, airbubbles present in the slurry adjusted into the given viscosity areeffectively removed so that air bubbles remaining in the slurry, inparticular, fine air bubbles having a level of 1 μm can be reduced asmuch as possible. Further the pore-forming agent powder, which isthermally decomposed at the time of the firing so as to make pores inthe substrate, can be more evenly dispersed into the slurry. Thereby itmakes the distribution of air permeability in the substrate planeslight. Moreover, the effect of ripening the slurry is also obtainedwith ease so that the slurry can be made more stable.

It is advisable to adjust the viscosity of the slurry into 40 to 100poise (25° C.). If the viscosity is less than 40 poise, the fluidity ofthe slurry is too high so that a substrate having a thickness of 1 mm ormore, in particular 2 mm or more, is not easily formed. Conversely, ifthe viscosity exceeds 100 poise, the viscosity is too high so that airbubbles remaining in the slurry, in particular, fine air bubbles havinga level of 1 μm are not easily reduced. From such a viewpoint, theslurry viscosity is more preferably from 50 to 80 poise (25° C.).

If the rotating speed of the stirring fans is below 5 rpm, air bubblespresent in the slurry is insufficiently removed and further it isdifficult to disperse the pore-forming agent powder evenly into theslurry. Consequently, it is indispensable to extend the above-mentionedkeeping time to 50 hours or more. Thus, this case is not practicable.

On the other hand, if the rotating speed is over 30 rpm, air is easilyincorporated into the slurry while the slurry is stirred. Inversely, airbubbles are easily generated.

From such a viewpoint, a more preferred rotating speed is from 5 to 20rpm. The shape of the stirring fans is not particularly limited.Preferable are stirring fans each having an anchor shape, which causesair mixture to be reduced.

If the time for keeping the rotation of the stirring fans is less than20 hours, air bubbles present in the slurry is insufficiently removedand further it is difficult to disperse the pore-forming agent powderevenly into the slurry. Conversely, if the time is made excessively longso as to be over 50 hours, a long time is required for the process.Thus, this case is unsuitable for practical use.

In order to make a scattering in the permeability between lots of thegreen sheets small in the above-mentioned process, it is advisable touse, as the slurry for producing the green sheets which become ceramicprecursors, a slurry obtained by: adding, to the viscosity-adjustedslurry which comprises the conductive component powder, the skeletoncomponent powder, the pore-forming agent powder, and the binder andobtained by defoaming the components under reduced pressure aftermilling the components to set the viscosity thereof into the range of 40to 100 poises (25° C.) and then keeping the resultant at roomtemperature while rotating the stirring fans in the slurry at a rotatingspeed of 5 to 30 rpm for 20 to 50 hours, a slurry which is subjected tothe same milling, has the same composition and has a viscosity notadjusted; defoaming the resultant mixture slurry under reduced pressureto adjust the viscosity into the range of 40 to 100 poise (25° C.); andthen keeping the resultant at room temperature while rotating thestirring fans in the slurry at a rotating speed of 5 to 30 rpm for 20 to50 hours.

In order to make a scattering in the green sheet lots smaller in thiscase, it is preferable to add 95 to 105 parts by mass of the total ofthe conductive component powder and the skeleton component powder in theslurry the viscosity of which is not adjusted to 100 parts by mass ofthe total of the conductive component powder and the skeleton componentpowder in the viscosity-adjusted slurry.

An instrument used for the defoaming under reduced pressure ispreferably a concentrating and stirring defoaming machine having arefrigerator and a collecting tank for collecting solvent and having aninternal volume of 10 liters or more, preferably 30 liters or more, morepreferably 50 liters or more. According to a separable flask having aninternal volume of less than 10 liters and having a cock for reducingpressure, or some other flask, which is used in ordinary laboratories, asubstrate having a sufficient quality intended in the present inventionis not easily obtained, probably, because of scale effect.

For satisfying the above-mentioned properties, important is the sizedistribution of particles in the slurry state used in the production ofa green sheet which becomes a ceramic precursor which becomes anelectrode support substrate, and it is important to use a slurry havingone peak in each of the ranges of 0.2 to 2 μm and of 3 to 50 μm in theparticle size distribution of the starting slurry for producing thegreen sheet.

In other words, the surface roughness of a support substrate isaffected, to some extent, by the above-mentioned particle sizeconstruction of the used starting materials. If coarse materials areused, the surface roughness of the resultant sintered body becomesrelatively coarse. If fine materials are used, the surface roughnessthereof becomes relatively dense. If a material having theabove-mentioned preferable particle size construction is used as each ofthe conductive component material powder and the skeleton componentmaterial powder which constitute the electrode support substrate, thissubstrate can easily have the above-mentioned proper porosity and amaximum roughness depth (Rmax) in the preferred range.

However, the present inventors have repeatedly made research so as tofind out following. A more important matter for obtaining a sinteredbody satisfying, in particular, the above-mentioned variationcoefficient of measured values of the gas permeable amounts and Rmaxdefined in the present invention is the particle size distribution ofsolid components contained in the slurry for obtaining a ceramic moldedbody which becomes a sintering material rather than the above-mentionedparticle size construction of the starting powders themselves. Moreover,when a slurry having one peak in each of the ranges of 0.2 to 2 μm andof 3 to 50 μm in the particle size distribution thereof is used toproduce a green sheet and then the sheet is fired, a sintered body(electrode support substrate) having a porosity of 20 to 50% and a Rmaxof 1.0 to 40 μm can be more surely obtained.

When the slurry is prepared, there is adopted a method of treating theabove-mentioned starting material blended suspension including thestarting powders in a ball mill or the like to knead and pulverize thepowders. Dependently on conditions for the kneading (examples of whichinclude the kind of a dispersing agent, and the added amount thereof), apart of the starting powders aggregates secondarily in thisslurry-preparing step and a part thereof is crushed. Therefore, theparticle size construction of the starting powders is not kept as it isin the particle size construction of solid components in the slurry.Thus, when the electrode support substrate of the present invention isproduced, it is important to adjust the particle size distribution ofthe slurry-state solid components used to produce a green sheet which isnot fired, as a factor which produces the largest effect on the porosityand the surface roughness of the electrode support substrate, to satisfythe above-mentioned requirements.

The particle size distributions of the solid components in the startingpowders and in slurry are values measured by the following methods. Theparticle size distribution of the starting powders is a measured valueafter using a laser diffraction manner particle size distribution meter“SALD-1100”, manufactured by Shimadzu Corp., using, as a dispersingmedium, an aqueous solution wherein 0.2% by mass of sodiummetaphosphoric acid is added as a dispersing agent to distilled water,adding 0.01 to 1% by mass of each of the starting powders to about 100cm³ of the dispersing medium, and treating the resultant with ultrasonicwaves for 3 to 10 minutes to disperse the powders. The particle sizedistribution of the solid components in each slurry is a measured valueafter using a solvent having the same composition as the solvent in theslurry, as a dispersing medium, adding the slurry to 100 cm³ of thedispersing medium into a concentration of 0.1 to 1% by mass, andtreating the resultant with ultrasonic waves for 3 to 10 minutes in thesame way to disperse the solid components. It is obtained as a particlesize distribution frequency graph as illustrated, for example, in FIG.4.

When the slurry having one peak in each of the ranges of 0.2 to 2 μm andof 3 to 50 μm in the particle size distribution thereof in the slurrystate as described above is used to form a green sheet, the formed greensheet is a green body wherein relatively fine particles having of 0.2 to2 μm size are filled into gaps between relatively coarse particles of 3to 50 μm size. When this is fired, a sintered body having the preferredsurface roughness can be obtained.

In order to ensure the above-mentioned preferable surface roughness, thecontent ratio by mass of the fine particles of 0.2 to 2 μm size to thecoarse particles of 3 to 50 μm size, in the slurry state thereof, ismore preferably from 20/80 to 90/10, even more preferably from 40/60 to80/20. The average particle size of the whole is preferably from 0.2 to5 μm, more preferably from 0.3 to 3 μm.

Means for adjusting the particle size distribution in the slurry stateinto the preferable range is not particularly limited, and examples ofordinary methods thereof are as following methods:

-   -   (i) a method of pre-firing a part of powders which are starting        materials at 900 to 1400° C. for 1 to 20 hours to make the        particle size thereof large, and then mixing the part with the        powders that are not fired,    -   (ii) a method of separating the addition of starting powders        into two stages when the starting powders and others are mixed        in a ball mill, and adding a part thereof after a given time        passes, thereby suppressing the degree of the pulverization, and    -   (iii) a method of kneading starting powders and others in two        kinds of ball mills having balls different in diameter to        prepare two slurries of different particle sizes, and then        mixing the two slurries.

The above-mentioned methods may be adopted alone. Alternatively, ifnecessary, two or more out of the methods can be appropriately combinedto be carried out.

For the electrode support substrate of the present invention, thefollowing method is adopted: a method of laying and spreading a slurryobtained as described above, which is comprised a ceramic startingpowder, a binder, and a dispersing medium, into an appropriate thicknessonto a supporting plate or a carrier sheet by a doctor blade method, acalendering method, an extrusion method or some other method so as to bemolded into a sheet form, drying this, volatilizing the dispersingmedium to yield a green sheet, adjusting the sheet into pieces of anappropriate size by cutting, punching or the like. The resulting sheetof an appropriate size put one of the pieces on a porous setter on ashelf board or put one of the pieces between setters as disclosed inRe-Publication Patent WO 99/59936, and heat and fire the piece in thisstate, at about 1100 to 1500° C., preferably about 1200 to 1450° C.,most preferably about 1250 to 1500° C. in the case of an anodicelectrode support substrate, under the atmosphere of air for about 1 to5 hours.

As the porous setter, there is preferably used a setter, for producing aporous ceramic sheet, which is made of a sheet-form ceramic bodycomprising 40 to 90% by mass of a (Ni) unit having a high gaspermeability so as to emit smoothly gas which is generated in a largeamount from the binder or the pore-forming agent when the green sheet isfired.

In the case that the electrode support substrate of the presentinvention is made practicable for a fuel cell, it is advisable to setthe thickness of the sheet to 0.3 mm or more, more preferably 0.5 mm ormore and set to 3 mm or less, more preferably 1 mm or less in order tosuppress electric conductance loss as much as possible while satisfyingrequired strength.

Incidentally, the burr height, which is very important for preventingcracking or breaking when the electrode support substrate receivesstacking-load or the like in the present invention, is remarkablychanged by the edge shape of a punching blade used when the green sheetis punched into a given size. It has been found out that when a punchingblade wherein the shape of its edge is wave-form is used, the height ofburrs formed on the punched-line of the green sheet can be suppressedinto a remarkably smaller value than in the case of using an ordinarystraight punching blade. The reasons for this would be as follows.

In the case that a straight punching blade is used, the whole of theblade edge contacts the green sheet in a linear form when the greensheet is cut with the blade. Simultaneously, tensile stress is linearlygenerated in the punching direction so that the cut face of the greensheet comes to be curled in the punching direction. Consequently, largeburrs are easily formed. On the other hand, in the case that a wave-formpunching blade is used, some parts of the blade edge (that is, thehighest points of the wave form) contact the green sheet in the form ofpoints. Therefore, the tensile stress in the punching direction isrelieved so that the degree of the curl becomes small. Thus, the burrheight would be remarkably lowered.

For example, FIG. 5 is an explanatory view for illustrating a punchingblade 1 used preferably in the present invention. A blade edge portion 1a is made into the form of the teeth of a saw. As described above, inorder to suppress the curl as much as possible at the time of punchingthe green sheet to make the burr height small, it is desired to form theblade edge portion 1 a as sharp as possible to make the blade edgeportion which firstly contacts the green sheet surface as small aspossible. Further, it set the angle α₁ of the blade edge (which meansthe angle of the wave-form blade edge portion when the blade is viewedfrom the side thereof) into the range of about 30 to 120 degrees, morepreferably about 45 to 90 degrees, set the height h of the blade intothe range of about 0.5 to 2 mm, more preferably about 0.5 to 1 mm, andset the pitch p into the range of about 0.2 to 7 mm, more preferablyabout 0.2 to 4 mm.

A preferred sectional structure of the punching blade 1 is asillustrated in FIG. 6. The angle α₂ of the blade edge (which means thetip angle of any section in the thickness direction of the blade) ispreferably from 20 to 70 degrees, more preferably from 20 to 50 degrees,and the thickness t of the edge is preferably from 0.3 to 1 mm, morepreferably from 0.4 to 0.7 mm.

For example, as illustrated in FIG. 7, the structure of the blade edgeis preferably made as follows: for a green sheet G to be punched, thestanding-up angle θ₁ on its Gx side (ordinarily, its internalcircumferential side) which will be a punched product is made acuterthan the standing-up angle θ₂ on its cut-off side G_(Y) side(ordinarily, its external circumferential side). The angle θ₁ ispreferably from 10 to 25 degrees, more preferably from 10 to 20 degrees,and the angle θ₂ is preferably from 10 to 35 degrees, more preferablyfrom 10 to 30 degrees. By use of the punching blade 1 having a bladeedge structure satisfying such angles, burrs formed on the externalcircumferential edge on the punched-product side can be made evensmaller.

In the illustrated example, the blade edge portion having a recurringstructure of the same pitch and the same shape is shown. However, theshape of the blade edge portion and the recurring units thereof are notlimited to the illustrated example. Of course, it is allowable to modifythe shape, the size or the like appropriately and carry out punching asfar as the blade structure is a structure suitable for suppressingburrs.

At the time of the punching, it is preferable to drop down the punchingblade 1 as perpendicularly as possible to a surface of the green sheet.In this case, it is desirable to sandwich and fix the green sheetbetween soft and elastic supporting plates not to be out of position.

For example, FIGS. 8 to 11 are explanatory schematic sectional viewsillustrating the structure of a punching member A used in the presentinvention, and a punching method using this. A punching blade 1 is fixedto a blade holder 2 with a hard member 3 and further a projecting plate4 made of a soft rubber or the like is fitted to the front end portionside of the hard member 3. The blade 1 is set not to penetrate throughthe projecting plate 4, so as not to project from the front end facethereof as far as the projecting plate 4 is not deformed by compression(see FIG. 8). In the illustrated example, illustrated is a structurewherein an elastic plate 6 is laminated also on the upper face of thehard plate 5 in a sheet supporting member B arranged oppositely to thepunching member A in order to ensure the fixation of a green sheet evenmore when the sheet is punched. However, the elastic plate 6 is notnecessarily essential. The green sheet G which is an object to bepunched is arranged on the supporting member B and then a punching workis performed.

When the green sheet G is punched, the punching member A is caused toapproach the surface of the green sheet G put on the sheet supportingmember B in the direction substantially perpendicular to the surface,from the state illustrated in FIG. 8. The punching blade 1 fitted intoin the punching member A is set not to project from the front face ofthe projecting plate 4 as described above. Therefore, when the punchingmember A is caused to approach the green sheet G as described above, theupper face of the sheet G firstly contacts the projecting plate 4 sothat the green sheet G is sandwiched from the upper and lower sidesbetween the projecting plate 4 and the elastic plate 6 (see FIG. 9).

Thereafter, the punching member A is further dropped down. As a result,the projecting plate 4 which is made of the elastic material iscompressed and deformed so that the punching blade 1 comes to projectout toward the green sheet G. Simultaneously, the green sheet G is urgedfrom both sides thereof by elastic force resulting from the elasticdeformation of the projecting plate 4 and elastic force, based on theplastic plate 6, from the lower face side of the sheet. Thus, the sheetG is supported and fixed, and in this state the blade 1 advances topunch the sheet (see FIG. 10).

After the punching blade 1 penetrates through the green sheet G so thatthe sheet is punched, the punching member A is backed up to move theblade 1 backwards from the green sheet G punched portion. In this step,similarly, the sandwich and fixation state is maintained by elasticforces of the projecting plate 4 and the elastic plate 6 until thepunching blade 1 is withdrawn from the green sheet G, and the state iscancelled after the punching blade 1 is withdrawn (see FIG. 11. in thefigure, y represents the punched portion).

In other words, a fall in the punching dimensional accuracy, based onpositional slippage, is prevented and additionally the generation ofburrs is restrained as much as possible since the punching andwithdrawing which follow the forward and backward movement of thepunching blade 1 are performed in the state that the green sheet G iselastically sandwiched and fixed.

Thus, when the present invention is carried out, a blade having awaver-form blade edge portion is used as a device for punching a greensheet, whereby the height of burrs formed in the punched-out portion canbe made as low as possible. As a result, when the resultant substratereceives stacking-load or the like, stress concentration on the burrsthereof can be suppressed as much as possible and the generation ofcracking or breaking can be suppressed into a minimum. In particular,the green sheet which becomes a precursor of the electrode supportsubstrate according to the present invention comprises a large amount ofa pore-forming agent in order to ensure given porosity, and the greensheet is softer than any green sheet used in the production of a densesintered body. Therefore, burrs generated when the green sheet ispunched into a given size easily become large. However, a punching bladeand a punching method as described above are adopted, whereby the burrscan be controlled as slightly as possible.

Clacking or breaking caused when the sheet substrate receivesstacking-load or the like may also be caused on the basis of largeprojections, undulations and so on that are present on the substratesurface besides the burrs. Therefore, in order to make the crackingresistance or breaking resistance thereof even higher, the projectionsor undulations should be made as small as possible as well as the burrheight is decreased. About a standard thereof, each of the largestprojection height and the largest undulation height is ⅓ or less of thethickness of the sheet, more preferably ¼ or less thereof, even morepreferably ⅕ or less thereof, as described above. The reason why theburr height, the largest projection height and the largest undulationheight are defined as the ratio thereof to the sheet thickness asdescribed above is that these values tend to be relatively larger as thesheet thickness is larger.

It appears that the largest cause that the projections are generatedwhen the porous electrode support substrate according to the presentinvention is produced is as follows. In the case that a granular aliensubstance is present on the shelf board or setter used when the greensheet is fired, the alien substance is caught in the green sheet, whichis put thereon, so that the sheet is hindered from being evenly shrunkin a flat state.

It also appears that the largest cause that the undulations aregenerated is as follows. When the binder or pore-forming agent in thegreen sheet is burned up so that the sheet is sintered, the contentthereof is too large or when the green sheets are put on each other andfired, the burning does not evenly advance with ease. Thus, a scatteringin the decomposed amount or burned amount thereof per unit time isgenerated so that the amount of generated decomposition gas becomesuneven. The shrinkage amount (about 10 to 30% of the length) of thegreen sheet generated when the sheet is fired is larger in thecircumferential edge portion than in the central portion of the sheet.Therefore, the undulations are easily generated in the circumferentialedge portion.

Thus, means for suppressing the projections into a minimum may be amethod of performing removal and cleaning sufficiently so that adheringparticles, fallen particles and others may not be present on the shelfboard or setter used in the firing. A specific and effective example ofmeans for suppressing the undulations in a minimum may be a method ofsuppressing the use of the binder or the pore-forming agent into aminimum and further firing the green sheets in the state that a poroussetter is put as a spacer in between the green sheets and a spacer for aweight is put onto the topmost portion, in particular when the greensheet are laminated and fired, so as to emit decomposition gas evenlyfrom the binder or the like.

When the electrode support substrate of the present invention is used asa member for a solid electrolyte type fuel cell, an anodic electrode anda thin electrolyte film are formed on a single surface of the substrate.The method for forming the electrode or the thin electrolyte film is notparticularly limited. The following can be appropriately used: a gasphase method, such as plasma spraying such as VSP, flame spraying, PVD(physical vapor deposition), magnetron sputtering, or electron beam PVD;or a wet method such as screen printing, sol-gel process, or slurrycoating. The thickness of the anodic electrode is usually from 3 to 300μm, preferably from 5 to 100 μm, and the thickness of the electrolytelayer is usually from 3 to 100 μm, preferably from 5 to 30 μm.

EXAMPLES

The following describes the present invention more specifically, givingworking examples and comparative examples. However, the presentinvention is not basically limited by the following working examples,and may be carried out with appropriate modification within a scopesuitable for the subject matters which have been described above andwill be described below. All of them are included in the technical scopeof the present invention.

Example 1

(Formation of Setters)

The following were mixed to produce a mixed powder as a startingmaterial: 40% by mass of 8% by mole yttrium oxide stabilized zirconiapowder (hereinafter referred to as the “8YSZ”) wherein the averageparticle size thereof was 0.5 μm and the particle size of the 90% volumethereof was 1.2 μm; and 60% by mass of nickel oxide powder obtained bydecomposing nickel carbonate powder thermally wherein the averageparticle size was 4.5 μm and the particle size of the 90% volume was 8μm.

To 100 parts by mass of this mixed powder were added 12 parts by mass ofan acrylic binder made of a copolymer obtained by use of 79.5% by massof isobutyl methacrylate, 20% by mass of 2-ethylhexyl methacrylate and0.5% by mass of methacrylic acid as monomer units, 40 parts by mass oftoluene and ethyl acetate (ratio by mass: 2/1) as solvents, and 2 partsby mass of dibutyl phthalate as a plasticizer. The mixture was kneadedin a ball mill and then defoamed, and the viscosity thereof wasadjusted, thereby yielding a slurry of 40 poise viscosity.

This slurry was fashioned into a sheet form by a doctor blade method,thereby forming green sheets, for setters, having a thickness of about0.5 mm. This was cut into a given size. Subsequently, the resultantswere put on a shelf board made of alumina and having a thickness of 20mm, and fired at 1400° C. for 5 hours to yield porous setters 17 cmsquare and about 0.4 mm thick, the porosity thereof being 15%.

(Formation of Electrode Support Substrate)

(1) Formation of Green Sheet for Electrode Support Substrate

Commercially available 3% by mole yttria-stabilized zirconia powder(trade name “HSY-3.0”, manufactured by Daichi Kigenso Kagaku Kogyo Co.,Ltd., particle size construction: particle size of the 50% byvolume=0.41 μm; and particle size of the 90% by volume=1.4 μm)(hereinafter referred to as the “3YSZ”) was pre-fired at 1200° C. underthe atmospheric of air for 3 hours. The following were put into a ballmill wherein alumina balls of 15 mm diameter were put: 20 parts by massof the pre-fired powder (particle size construction: particle size ofthe 50% by volume=14 μm; and particle size of the 90% by volume=29 μm),20 parts by mass of the above-mentioned zirconia powder not pre-fired,60 parts by mass of nickel oxide powder (manufactured by KishidaChemical Co., Ltd., particle size construction: particle size of the 50%by volume=0.6 μm; and particle size of the 90% by volume=2.7 μm), 10parts by mass of corn starch (manufactured by Kanto Chemical Co., Inc.),15 parts by mass of a methacrylic acid based copolymer (molecularweight: 30,000, glass transition temperature: −8° C.) as a binder, 2parts by mass of dibutyl phthalate as a plasticizer, and 50 parts bymass of a mixed solvent of toluene and isopropyl alcohol (ratio by mass:3/2) as a dispersing medium. The mixture was kneaded at about 60 rpm for20 hours to prepare a slurry.

The particle size distribution of the resultant slurry was measured witha laser diffraction manner particle size distribution meter (trade name“SALD-1100”, manufactured by Shimadzu Corp.), and the resultantfrequency graph of the particle size distribution was observed. As aresult, two peaks were observed in a section of 0.2 to 0.3 μm and asection of 4 to 5 μm, and the content ratio of fine particles in therange of 0.2 to 2 μm and coarse particles in the range of 3 to 50 μm was82/18.

This slurry was put into a pressure-reducing defoaming machine,concentrated and defoamed to adjust the viscosity into 50 poise (25°C.). Anchor-shaped stirring fans immersed in the slurry were rotated ata rotating speed of 10 rpm for 24 hours, and finally the slurry waspassed through a 200-mesh filter. The resultant was applied onto apolyethylene terephthalate (PET) film by a doctor blade method. At thistime, a gap based on a blade was adjusted to form a green sheet having athickness of about 0.59 mm.

(2) Punching and Firing of Green Sheet for Electrode Support Substrate

The green sheet obtained as described above was punched into a piece 15cm square by the method as illustrated in FIGS. 8 to 11 using a punchingblade (manufactured by Nakayama Shiki Zairyo Co., Ltd.) having awave-form blade edge (in the form of the teeth of a saw as illustratedin FIGS. 5 to 7) and having blade edge angles α₁ and α₂ of 60° and 45°,respectively, blade edge angles θ₁ and θ₂ of 15° and 30°, respectively,a blade width t of 0.7 mm, a blade height h of 1 mm, and a pitch p of1.1 mm.

The upper and lower faces of the punched substrate green sheet weresandwiched between the setters produced as described above so as not toforce out the circumferential edge of the green sheet therefrom. Thenthe resultant was put onto a shelf board (trade name: “Dialight DC-M”,manufactured by Tokai Konetsu Kogyo Co., Ltd.) having a thickness of 20mm and fired at 1300° C. for 3 hours to yield an electrode supportsubstrate about 12.5 cm square and about 0.5 mm thick.

Example 2

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, a slurry having no adjusted viscosity, obtainedby treatment with a ball mill in the same way as in Example 1, and aslurry having a viscosity adjusted to 50 poise with thepressure-reducing defoaming machine were prepared. The slurry having noadjusted viscosity was added to the slurry having the adjustedviscosity. At this time, the addition was performed to make the totalmass of the 3YSZ powder and the nickel oxide powder in the slurry havingthe adjusted viscosity equal to the total mass of the 3YSZ powder andthe nickel oxide powder in the slurry having no adjusted viscosity.

Next, the viscosity of the mixed slurry was adjusted to 50 poise (25°C.) by pressure-reducing defoaming in the same way. The slurry was keptat room temperature while stirring fans in the slurry were rotated at arotating speed of 12 rpm for 20 hours. The resultantgreen-sheet-producing slurry was used and fashioned into a sheet form.Thus, a green sheet having a thickness of about 0.59 mm was yielded.

Subsequently, in the same way as in Example 1, punching and firing wereperformed to yield an electrode support substrate about 12.5 cm squareand about 0.5 mm thick.

Example 3

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, the viscosity of the slurry was adjusted to 60poise by pressure-reducing defoaming. The slurry was kept at roomtemperature while the stirring fans were rotated at a rotating speed of18 rpm for 30 hours. Subsequently, a gap based on the doctor blade wasadjusted to form a green sheet having a thickness of 0.35 mm. In thevery same way as in Example 1 except the above, an electrode supportsubstrate about 12.5 cm square and about 0.3 mm thick was yielded.

Example 4

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, 10 parts by mass of corn starch (manufacturedby Kanto Chemical Co., Inc.), 15 parts by mass of a binder made ofmethacrylic copolymer and 2 parts by mass of dibutyl phthalate as aplasticizer, the latter two of which were the same as in Example 1, wereused for 15 parts by mass of pre-fired powder (particle sizeconcentration: diameter of the 50% volume=20 μm; and diameter of the 90%volume=41 μm) obtained by pre-firing 8YSZ powder (particle sizeconcentration: diameter of the 50% volume=0.5 μm; and diameter of the90% volume=1.2 μm) at 1200° C. under the atmosphere of air for 3 hours,and 15 parts by mass of the above-mentioned powder not pre-fired, and 70parts by mass of nickel oxide (manufactured by Seido Chemical IndustryCo., Ltd., particle size concentration: diameter of the 50% volume=0.8μm; and diameter of the 90% volume=2.1 μm). In the same way as inExample 1 except the above, a green sheet for a substrate was formed,and subsequently punching and firing were performed in the same way toyield an electrode support substrate about 12.5 cm square and about 0.5mm thick.

Example 5

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, 10 parts by mass of corn starch (manufacturedby Kanto Chemical Co., Inc.), 15 parts by mass of a binder made ofmethacrylic copolymer and 2 parts by mass of dibutyl phthalate as aplasticizer, the latter two of which were the same as in Example 1, wereused for 20 parts by mass of pre-fired powder obtained by pre-firingcommercially available 3YSZ powder (ditto) at 1200° C. under theatmosphere of air for 3 hours, 10 parts by mass of the above-mentionedpowder not pre-fired, and 70 parts by mass of nickel oxide (manufacturedby Kishida Chemical Co., Ltd.). In the same way as in Example 1 exceptthe above, a green sheet for a substrate was formed, and subsequentlypunching and firing were performed in the same way to yield an electrodesupport substrate about 12.5 cm square and about 0.5 mm thick.

Example 6

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, 20 parts by mass of corn starch (manufacturedby Kanto Chemical Co., Inc.), 15 parts by mass of a binder made ofmethacrylic copolymer and 2 parts by mass of dibutyl phthalate as aplasticizer, the latter two of which were the same as in Example 1, wereused for 15 parts by mass of pre-fired powder obtained by pre-firingcommercially available 3YSZ powder (ditto) at 1200° C. under theatmosphere of air for 3 hours, and 15 parts by mass of theabove-mentioned powder not pre-fired, and 70 parts by mass of nickeloxide (manufactured by Seido Chemical Industry Co., Ltd.). In the sameway as in Example 1 except the above, a green sheet for a substrate wasformed, and subsequently punching and firing were performed in the sameway to yield an electrode support substrate about 12.5 cm square andabout 0.5 mm thick.

Comparative Example 1

In Example 1, the viscosity was adjusted to 50 poise (25° C.), andimmediately after this the slurry was passed through a 200-mesh filterwithout keeping the slurry at room temperature while stirring theslurry. Subsequently, the slurry was applied onto a PET film by a doctorblade method so as to form a green sheet about 0.59 mm thick similarly.Furthermore, in the same way as in Example 1, an electrode supportsubstrate about 12.5 cm square and about 0.5 mm thick was produced.

Comparative Example 2

In Example 1, the viscosity was adjusted to 120 poise (25° C.), andsubsequently stirring fans were immersed into the slurry. The stirringfans in the slurry were rotated at a rotating speed of 10 rpm for 10hours. Thereafter, the slurry was passed through a 200-mesh filter andthen the slurry was applied onto a PET film by a doctor blade method soas to form a green sheet about 0.59 mm thick similarly. Furthermore, inthe same way as in Example 1, an electrode support substrate about 12.5cm square and about 0.5 mm thick was produced.

Comparative Example 3

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, the same materials were used except that the1200° C. pre-fired powder made of the commercially available 3YSZ powder(ditto) was not used and 40 parts by mass of the 3YSZ powder (ditto)were used. The materials were put into a ball mill in which zirconiaballs of 5 mm diameter were charged, and kneaded at about 50 rpm for 3hours to prepare a slurry. In the same way as in the item 1) of Example1 except the above, a green sheet of about 0.59 mm thickness was formed.Furthermore, in the same way as in Example 1, an electrode supportsubstrate about 12.5 cm square and about 0.5 mm thick was formed.

Comparative Example 4

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Example 1, the same materials were used except that the3YSZ powder (ditto) was not used and the following were used: 40 partsby mass of 3YSZ powder pre-fired at 1200° C. for 3 hours and 60 parts bymass of powder obtained by pre-firing nickel oxide powder (manufacturedby Kishida Chemical Co., Ltd.) at 1100° C. in the atmosphere of air for3 hours (particle size concentration: diameter of the 50% volume=17 μm;and diameter of the 90% volume=30 μm). The materials were put into aball mill in which alumina balls of 20 mm diameter were charged, andkneaded at about 40 rpm for 10 hours to prepare a slurry. In the sameway as in the item 1) of Example 1 except the above, a green sheet ofabout 0.59 mm thickness was formed. Furthermore, in the same way as inExample 1, an electrode support substrate about 12.5 cm square and about0.5 mm thick was formed.

Comparative Example 5

In Comparative Example 1, the conditions for ripening the slurry waschanged as follows: 2 rpm×2 hours. In the item “(2) Punching of GreenSheet for Substrate”, a single edge blade (manufactured by NakayamaShiki Zairyo Co., Ltd.) having a straight blade edge having a thicknesst of 0.7 mm and an blade edge angle α₂ of 45° was used to punch thesheet into a piece 15 cm square. In the very same way except the above,punching and firing were performed to form an electrode supportsubstrate.

Comparative Example 6

In the item “(1) Formation of green sheet for electrode supportsubstrate” in Comparative Example 1, 25 parts by mass of the binder madeof the methacrylic acid based copolymer were used and further theconditions for ripening the slurry was changed as follows: 2 rpm×54hours. Additionally, in the item 2) Firing of Green Sheet for Substratetherein, the electrode-substrate-forming green sheet was fired withoutputting any setter thereon and further the following was used as thesetter for underlay: a setter wherein about ten adhering particleshaving a diameter of about 0.5 to 2 mm were observed per 100 Cm². In thesame way as the above-mentioned example except the above, an electrodesupport substrate was formed.

Performance Tests

Each of the electrode support substrates obtained in Examples 1 to 6 andComparative Examples 1 to 6 was used to make the following performanceevaluating tests. The results are shown in Tables 1 to 6.

(1) Gas Permeable Test

The electrode support substrate about 12.5 cm square and about 0.5 mmthick, which was obtained as described above, was cut into 16 pieces 3cm square with a diamond cutter fitted to a ceramic grinder(manufactured by Marutoh Co., Ltd.). These were used as permeabilitytesting pieces.

Any one of the testing pieces was set to a permeability testing machine(trade name: “KES-F8-AP1”, manufactured by Kato Tech Co., Ltd.), towhich an assistant member for holding a sample was fitted. This testingmachine is a machine which has a mechanism wherein a constant flow rateof air is sent to the test piece by piston movement of a plunger and acylinder to emit the air into the atmosphere or absorb air therefrom,and which is capable of measuring the pressure loss based on the samplewith a differential pressure semiconductor gauge within 10 seconds percycle and showing the gas permeation resistance (the reciprocal numberof the gas permeability) of the sample directly with a digital panelmeter. The size of the sample piece was 3 cm square, and both endsthereof were necessary by 0.5 mm for holding the sample piece.Therefore, the effective area thereof was 2 cm square (area: 4 cm²). Theoutline of the machine is illustrated in FIG. 12 (in this figure, Srepresents the sample; 11, a compressor; 12, a flow rate meter; and 13,a differential pressure meter).

About each of the 16 sample pieces, the gas permeability thereof wasmeasured. The average value and the standard deviation were obtained,and further the variation coefficient was obtained.

(2) Measurement of Porosity

The porosities of the electrode support substrate obtained as describedabove were measured with an automatic porosimeter (trade name: “AutoporeIII9240”, manufactured by Shimadzu Corp.).

(3) Surface Roughness

A laser optical manner non-contact three-dimensional shape measuringdevice (trade name: “Micro-focus Expert UBM-14 model”, manufactured byUBM Co.) was used to measure the maximum roughness depths (Rmax) of thefront and rear faces (the side contacting the PET surface when the greensheet was formed is referred as the front side) of each of the electrodesupport substrates at a pitch of 0.1 mm.

Simultaneously, burrs on the circumferential edge of each of theelectrode support substrates, and projections and undulations on thesurface were measured.

(4) Load Test

Each of the sample substrates was arranged on an aluminaunderlying-plate in the state that the substrate was sandwiched betweentwo alumina plates (trade name: “SSA-S1”, manufactured by Nikkato Co.,Ltd.), the surfaces of which were smooth and had kept parallelism, andthen a load of 0.2 kg/cm² was applied onto the entire surface of thesubstrate. In this state, the temperature of the substrate was raisedfrom room temperature to 1000° C. over 10 hours, and kept at 1000° C.for 1 hour, and then dropped to room temperature. This operation wasrepeated ten times to obtain the generation frequency of cracking orbreaking. It was judged with the naked eye whether or the cracking orbreaking was generated.

(5) Observation of Cell Printed Interface

The states of the interfaces between each of the electrode supportsubstrates and an anodic electrode and between each of the electrodesupport substrates and an electrolyte layer were observed from an SEMphotograph thereof.

(Formation of Cell)

(a) Preparation of Paste

To 100 parts by mass of 10% by mole scandia- and 1% by moleceria-stabilized zirconia powder (manufactured by Daichi Kigenso KagakuKogyo Co., Ltd.) were added 350 parts by mass of turpentine oil and 2parts by mass of ethylcellulose as a binder. Then, the mixture waskneaded in a planetary mill for 2 hours to yield a slurry. The slurrywas used as an electrolyte paste.

To 50 parts by mass of 3YSZ powder (ditto) and 50 parts by mass ofnickel oxide (manufactured by Kishida Chemical Co., Ltd.) were added 350parts by mass of turpentine oil and 2 parts by mass of ethylcellulose asa binder. Then, the mixture was kneaded in a planetary mill for 2 hoursto yield a slurry. The slurry was used as an anode paste.

To 100 parts by mass of La_(0.8)Sr_(0.2)MnO₃ powder (manufactured bySeimi Chemical Co., Ltd.) were added 350 parts by mass of turpentine oiland 2 parts by mass of ethylcellulose as a binder. Then, the mixture waskneaded in a planetary mill for 2 hours to yield a slurry. The slurrywas used as a cathode paste.

(b) Formation of Cell

Next, the anode paste was printed onto one surface of theabove-mentioned electrode support substrate by screen printing. Theresultant was dried at 100° C. for 1 hour and fired at 1350° C. for 2hours to form an anode layer on the electrode support substrate, therebyforming an anode-layer-attached electrode support substrate (AS-A).

The electrolyte paste was printed on the anode layer of theanode-layer-attached electrode support substrate (AS-A) by screenprinting. The resultant was dried at 100° C. for 1 hour and fired at1350° C. for 2 hours to form a half cell wherein the anode layer and anelectrolyte layer were formed on the electrode support substrate(AS-A-E).

Finally, the cathode paste was applied onto the electrolyte layer ofthis half cell by screen printing. The resultant was dried at 100° C.for 1 hour and fired at 1300° C. for 2 hours to form a cell wherein theanode layer, the electrolyte layer and a cathode layer were formed onthe electrode support substrate (AS-A-E-C). The electrode area of thecell was about 121 cm².

(c) An electrolyte layer, an anode layer, and a cathode layer wereformed on the electrode support substrate about 12.5 cm square and about0.5 mm thick, obtained in each of the Examples and the ComparativeExamples, by screen printing in accordance with the method described inthe item (Formation of cell), so as to produce an anode-layer-attachedelectrode support substrate (AS-A) and a half cell (AS-A-E). The surfaceof each thereof was observed with the naked eye. Further the state ofthe printed interface was observed from an SEM photograph thereof. Inthis way, the state of the interface between the electrode supportsubstrate and the anode layer, the state of the interface between theanode layer and the electrolyte layer, and the state of the electrolytelayer were examined.

(6) Power Generation Test

Furthermore, in a single cell power generation test device using thecell (AS-A-E-C) produced in accordance with the method described in theitem (Formation of cell), humidified hydrogen and air were used as afuel and an oxidizer, respectively, to make a power generation test at apower generation temperature of 800° C. for 24 hours. The highest powerdensity at the initial of the test and the highest power density after24 hours from the start of the test were obtained so as to calculate thedecreasing rate of the highest power.

The results are shown in Tables 1 to 6 TABLE 1 Example 1 Example 2Example 3 Composition NiO/3YSZ + NiO/3YSZ + NiO/3YSZ + pre-sinteredpre-sintered pre-sintered 3YSZ/starch 3YSZ/starch 3YSZ/starch 60/20 +20/10 60/20 + 20/10 60/20 + 20/10 Peak sections in slurry 0.2 to 0.3 μmand 0.2 to 0.3 μm and 0.2 to 0.3 μm and particle size distribution 4 to5 μm 4 to 5 μm 4 to 5 μm Content ratio of fine 82/18 82/18 82/18particles to coarse particles Slurry viscosity (poise) 50 50 60Conditions for keeping 10 rpm × 24 hours 12 rpm × 20 hours 18 rpm × 30hours slurry at room temperature Green sheet thickness (mm) 0.59 0.590.35 Punching die Wave form Wave form Wave form Support substratethickness 0.5 0.5 0.3 (mm) Porosity (%) 25 23 27 Burr height/substrate0.30 0.27 0.34 thickness Undulation 0.13 0.11 0.17 height/substratethickness Projection height/substrate 0.15 0.12 0.17 thickness

TABLE 2 Example 4 Example 5 Example 6 Composition NiO/8YSZ + NiO/3YSZ +NiO/3YSZ + pre-sintered pre-sintered pre-sintered 8YSZ/starch3YSZ/starch 3YSZ/starch 70/15 + 15/10 70/20 + 10/10 70/15 + 15/20 Peaksections in slurry 0.2 to 0.3 μm and 0.2 to 0.3 μm and 0.2 to 0.3 μm andparticle size distribution 5 to 6 μm 4 to 5 μm 4 to 5 μm Content ratioof fine 86/14 82/18 Dec-88 particles to coarse particles Slurryviscosity (poise) 50 70 50 Conditions for keeping 10 rpm × 24 hours 10rpm × 24 hours 10 rpm × 24 hours slurry at room temperature Green sheetthickness (mm) 0.59 0.59 0.59 Punching die Wave form Wave form Wave formSupport substrate thickness 0.5 0.5 0.5 (mm) Porosity (%) 28 28 32 Burrheight/substrate 0.41 0.32 0.36 thickness Undulation 0.11 0.15 0.13height/substrate thickness Projection height/substrate 0.12 0.17 0.14thickness

TABLE 3 Comparative Comparative Comparative Example 1 Example 2 Example3 Composition NiO/3YSZ + NiO/3YSZ + NiO/3YSZ/starch pre-sinteredpre-sintered 60/40/10 3YSZ/starch 3YSZ/starch 60/20 + 20/10 60/20 +20/10 Peak sections in slurry 0.2 to 0.3 μm and 0.2 to 0.3 μm and Only0.2 to particle size distribution 4 to 5 μm 4 to 5 μm 0.3 μm Contentratio of fine 82/18 82/18 — particles to coarse particles Slurryviscosity (poise) 50 120 40 Conditions for keeping Nothing 10 rpm × 10hours 50 rpm × 3 hours slurry at room temperature Green sheet thickness(mm) 0.59 0.59 0.59 Punching die Wave form Wave form Wave form Supportsubstrate thickness 0.5 0.5 0.5 (mm) Porosity (%) 25 29 28 Burrheight/substrate 0.33 0.37 0.39 thickness Undulation 0.14 0.19 0.21height/substrate thickness Projection height/substrate 0.15 0.26 0.12thickness

TABLE 4 Comparative Comparative Comparative Example 4 Example 5 Example6 Composition Pre-sintered NiO/3YSZ + NiO/3YSZ + NiO/pre-sinteredpre-sintered pre-sintered 3YSZ/starch 3YSZ/starch 3YSZ/starch 60/40/1060/20 + 20/10 60/20 + 20/10 Peak sections in slurry Only 7 to 0.2 to 0.3μm and 0.2 to 0.3 μm and particle size distribution 8 μm 4 to 5 μm 4 to5 μm Content ratio of fine — 82/18 82/18 particles to coarse particlesSlurry viscosity (poise) 80 50 50 Conditions for keeping 40 rpm × 10hours 2 rpm × 2 hours 2 rpm × 54 hours slurry at room temperature Greensheet thickness (mm) 0.59 0.59 0.59 Punching die Wave form Linear Waveform Support substrate thickness 0.5 0.5 0.5 (mm) Porosity (%) 37 26 26Burr height/substrate 0.24 0.68 0.42 thickness Undulation 0.14 0.31 0.35height/substrate thickness Projection height/substrate 0.19 0.28 0.38thickness

TABLE 5 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Crack generation 0 0 0 0 5 0 frequency (%/in 20 sheets) Surfaceroughness (μm) Front face Rmax 4.15 2.89 3.74 18.13 5.57 3.11 Rear faceRmax 3.97 3.13 3.61 22.09 3.96 3.83 Gas permeability test (mL/min-kPa)Gas permeability 33 28 62 41 30 30 maximum value Gas permeability 19 1845 23 19 19 minimum value Average value 23 23 54 32 15 24 Standarddeviation 2.1 1.7 8.3 3.7 1.9 2.5 Variation coefficient 9 7 15 12 13 10Anode formation Interface between Close adhesion Close adhesion Closeadhesion Close adhesion Close adhesion Close adhesion substrate andanode Electrolyte formation Interface between Close adhesion Closeadhesion Close adhesion Close adhesion Close adhesion Close adhesionanode and electrolyte State of electrolyte Substantially SubstantiallySubstantially Substantially Substantially Substantially thickness eveneven even even even even Power generation performance Highest-power 8 67 11 14 9 decreasing rate (%) Crack after the test Not generated Notgenerated Not generated Not generated Not generated Not generated

TABLE 6 Comparative Comparative Comparative Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Crack generation 0 5 10 45 26 36 frequency (%/in 20 sheets) Surfaceroughness (μm) Front face Rmax 4.36 3.84 4.75 47.3 3.42 3.86 Rear faceRmax 4.19 4.33 4.96 45.8 3.06 4.11 Gas permeability test (mL/min-kPa)Gas permeability 35 30 33 43 35 33 maximum value Gas permeability 12 915 17 14 13 minimum value Average value 20 21 21 24 23 19 Standarddeviation 6.6 5.5 5.9 5.5 7.1 4.2 Variation coefficient 33 26 28 23 3122 Anode formation Interface between Close adhesion Close adhesionExfoliation Partial Close adhesion Partial substrate and anodeexfoliation exfoliation Electrolyte formation Interface between Closeadhesion Close adhesion Close adhesion Partial Close adhesion Closeadhesion anode and electrolyte exfoliation State of electrolyteSubstantially Substantially Substantially Uneven SubstantiallySubstantially thickness even even even even even Power generationperformance Highest-power 35 23 28 31 18 20 decreasing rate (%) Crackafter the test Generated Generated Generated Generated GeneratedGenerated

INDUSTRIAL APPLICABILITY

The present invention is constructed as described above, and comprises aceramic sheet having appropriate porosity, thickness and surface area.In particular, the variation coefficient of measured values of the gaspermeable amounts thereof is set into a given range and further thesurface roughness measured with a laser optical manner three-dimensionalshape measuring device is controlled, as the maximum roughness depththereof, into a specific range, thereby making it possible to provide anelectrode support substrate wherein a dense, even and highly-adhesiveprinted electrode can be formed while even and superior gaspermeability/diffusibility can be ensured, the substrate havingperformances eminent for a solid oxide type fuel cell.

Furthermore, the height of burrs, and the height(s) of undulationsand/or projections, which are measured with the same laser opticalmanner three-dimensional shape measuring device, are specified, therebymaking it possible to provide an electrode support substrate for givinga high-performance fuel cell capable of suppressing cracking or brakingbased on local stress concentration when stacking-load is applied to thecell and capable of resisting thermal shock, thermal stress and others.

1. A electrode support substrate for solid oxide type fuel cellcharacterized in comprising a ceramic sheet having a porosity of 20 to50%, a thickness of 0.2 to 3 mm and a surface area of 50 cm² or more,and the variation coefficient of measured values of the gas permeableamounts of any area of 4 cm² selected optionally from the whole of thesurface area of the substrate, the values being measured by the methodaccording to JIS K 6400, is from 5 to 20%.
 2. The electrode supportsubstrate according to claim 1, wherein a surface roughness thereofmeasured with a laser optical manner three-dimensional shape measuringdevice is 1.0 to 40 μm as the maximum roughness depth (Rmax: GermanStandard “DIN 4768”).
 3. The electrode support substrate according toclaim 1, wherein height of burrs thereof measured with a laser opticalmanner three-dimensional shape measuring device is ½ or less of thethickness of the sheet.
 4. The electrode support substrate according toclaim 1, wherein largest height(s) of undulations and/or projectionsmeasured with a laser optical manner three-dimensional shape measuringdevice is/are ⅓ or less of a thickness of the sheet.
 5. A producingprocess of the electrode support substrate of sheet form for solid oxidetype fuel cell according to claim 1 characterized in comprising steps:using a slurry for producing of green sheet becoming a ceramicprecursor, including an conductive component powder, an skeletoncomponent powder, a pore-forming agent powder and a binder, defoamedunder reduced pressure after milling to adjust the viscosity thereof to40 to 100 poise (25° C.), and kept at room temperature while rotatingstirring fans therein at a rotating speed of 5 to 30 rpm for 20 to 50hours; fashioning the slurry into a sheet by a doctor blade method toobtain a green sheet; cutting the green sheet into a given shape; andthen firing the green sheet having the given shape.
 6. The processaccording to claim 5, wherein particle size distribution of the slurryhas a peak in each of ranges of 0.2 to 2 μm and 3 to 50 μm, and acontent ratio by mass of fine particles in the range of 0.2 to 2 μm tocoarse particles in the range of 3 to 50 μm is in a range of 20/80 to90/10.
 7. The process according to claim 5 for producing the electrodesupport substrate for solid oxide type fuel cell comprising the porousceramic, wherein there is used the slurry including 5 to 30 parts bymass of the binder and 2 to 40 parts by mass of the pore-forming agentpowder with respect to 100 parts by mass of the total of the conductivecomponent powder and the skeleton component powder.
 8. The processaccording to claim 5, wherein the green sheet is punched into givenshape by use of a punching blade having a waver-form blade edge, andthen is fired.
 9. The process according to claim 8, wherein the punchingblade is used of which the angle (α₁), (α₂), (θ₁) and (θ₂) thereofsatisfy the following relationship:α₁=30 to 120°, 20°≦α₂=θ₁+θ₂≦70°, and θ₁≦θ₂, the angle (α₁) meaning ofangle being viewed from the side face of the wave-form blade, the angle(α₂) meaning of blade edge angle of the cross section of the blade, theangle (θ₁) meaning of angle made between the surface thereof on the sideof the sheet becoming a product and a center line (x) passing throughthe blade edge, the angle (θ₂) meaning of angle made between the surfacethereof on the side of the rest of the sheet and the center line (x)passing through the blade edge.
 10. The electrode support substrateaccording to claim 2, wherein height of burrs thereof measured with alaser optical manner three-dimensional shape measuring device is ½ orless of the thickness of the sheet.
 11. The electrode support substrateaccording to claim 2, wherein largest height(s) of undulations and/orprojections measured with a laser optical manner three-dimensional shapemeasuring device is/are ⅓ or less of a thickness of the sheet.
 12. Theelectrode support substrate according to claim 3, wherein largestheight(s) of undulations and/or projections measured with a laseroptical manner three-dimensional shape measuring device is/are ⅓ or lessof a thickness of the sheet.
 13. A producing process of the electrodesupport substrate of sheet form for solid oxide type fuel cell accordingto claim 2 characterized in comprising steps: using a slurry forproducing of green sheet becoming a ceramic precursor, including anconductive component powder, an skeleton component powder, apore-forming agent powder and a binder, defoamed under reduced pressureafter milling to adjust the viscosity thereof to 40 to 100 poise (25°C.), and kept at room temperature while rotating stirring fans thereinat a rotating speed of 5 to 30 rpm for 20 to 50 hours; fashioning theslurry into a sheet by a doctor blade method to obtain a green sheet;cutting the green sheet into a given shape; and then firing the greensheet having the given shape.
 14. A producing process of the electrodesupport substrate of sheet form for solid oxide type fuel cell accordingto claim 3 characterized in comprising steps: using a slurry forproducing of green sheet becoming a ceramic precursor, including anconductive component powder, an skeleton component powder, apore-forming agent powder and a binder, defoamed under reduced pressureafter milling to adjust the viscosity thereof to 40 to 100 poise (25°C.), and kept at room temperature while rotating stirring fans thereinat a rotating speed of 5 to 30 rpm for 20 to 50 hours; fashioning theslurry into a sheet by a doctor blade method to obtain a green sheet;cutting the green sheet into a given shape; and then firing the greensheet having the given shape.
 15. A producing process of the electrodesupport substrate of sheet form for solid oxide type fuel cell accordingto claim 4 characterized in comprising steps: using a slurry forproducing of green sheet becoming a ceramic precursor, including anconductive component powder, an skeleton component powder, apore-forming agent powder and a binder, defoamed under reduced pressureafter milling to adjust the viscosity thereof to 40 to 100 poise (25°C.), and kept at room temperature while rotating stirring fans thereinat a rotating speed of 5 to 30 rpm for 20 to 50 hours; fashioning theslurry into a sheet by a doctor blade method to obtain a green sheet;cutting the green sheet into a given shape; and then firing the greensheet having the given shape.
 16. The process according to claim 6 forproducing the electrode support substrate for solid oxide type fuel cellcomprising the porous ceramic, wherein there is used the slurryincluding 5 to 30 parts by mass of the binder and 2 to 40 parts by massof the pore-forming agent powder with respect to 100 parts by mass ofthe total of the conductive component powder and the skeleton componentpowder.
 17. The process according to claim 6, wherein the green sheet ispunched into given shape by use of a punching blade having a waver-formblade edge, and then is fired.
 18. The process according to claim 7,wherein the green sheet is punched into given shape by use of a punchingblade having a waver-form blade edge, and then is fired.